Source 1review2000Journal of the American Society of Nephrology
Toolkit/Xenopus oocyte expression system
Xenopus oocyte expression system
Also known as: Xenopus oocyte expression assay
Taxonomy: Technique Branch / Method. Workflows sit above the mechanism and technique branches rather than replacing them.
Summary
The Xenopus oocyte expression system has proven to be a valuable method for functional analysis of candidate water channel RNAs, since the oocytes normally exhibit low membrane water permeability.
Usefulness & Problems
Why this is useful
This assay expresses candidate water-channel RNAs in Xenopus oocytes and tests whether membrane water permeability increases. The review uses it as a functional readout for aquaporin activity.; functional analysis of candidate water channel RNAs; testing whether a candidate channel increases membrane water permeability; comparing channel-dependent swelling against low-permeability controls
Source:
This assay expresses candidate water-channel RNAs in Xenopus oocytes and tests whether membrane water permeability increases. The review uses it as a functional readout for aquaporin activity.
Source:
functional analysis of candidate water channel RNAs
Source:
testing whether a candidate channel increases membrane water permeability
Source:
comparing channel-dependent swelling against low-permeability controls
Problem solved
It solves the problem of functionally testing candidate water channels in a system with low endogenous water permeability.; providing a low-background heterologous system for water-channel functional testing
Source:
It solves the problem of functionally testing candidate water channels in a system with low endogenous water permeability.
Source:
providing a low-background heterologous system for water-channel functional testing
Problem links
providing a low-background heterologous system for water-channel functional testing
LiteratureIt solves the problem of functionally testing candidate water channels in a system with low endogenous water permeability.
Source:
It solves the problem of functionally testing candidate water channels in a system with low endogenous water permeability.
Published Workflows
Objective: Identify and functionally validate molecular water channels responsible for renal and other biologic membrane water permeability.
Why it works: The review describes a progression from candidate identification to heterologous functional testing and then purified-protein reconstitution, allowing investigators to move from correlation to direct demonstration of channel activity and selectivity.
channel-mediated transmembrane water transportheterologous expression for functional testingpurified-protein reconstitution for sufficiency testingbiochemical purificationfunctional reconstitutionexpression cloningXenopus oocyte expressionproteoliposome biophysics
Stages
- 1.Candidate identification from purification, cloning, and tissue distribution(library_design)
The review indicates that water transporters were unknown and candidate molecules had to be recognized before direct functional testing.
Selection: Proteins are prioritized when they are purified, sequenceable or clonable, and abundant in highly water-permeable tissues.
- 2.Heterologous functional assay in Xenopus oocytes(functional_characterization)
The oocyte system provides a low-background functional test for candidate water channel RNAs.
Selection: Candidates are advanced if expression in oocytes increases water permeability relative to water-injected controls.
- 3.Purified-protein reconstitution and direct biophysical confirmation(confirmatory_validation)
This stage tests whether the purified protein alone is sufficient to account for water permeability and whether transport is selective.
Selection: Purified candidate protein is reconstituted into phospholipid vesicles and compared with protein-free liposomes for direct permeability and selectivity measurements.
Steps
- 1.Purify and sequence a candidate membrane protein to enable cDNA cloning
Generate a molecular candidate for water-channel testing.
The review indicates that the molecular identity of water transporters was unknown, so a candidate first had to be isolated and cloned before functional assays could be performed.
- 2.Express candidate water-channel RNA in Xenopus oocytes and test osmotic swellingfunctional assay platform
Determine whether the candidate confers water permeability in a low-background system.
The review explicitly states that oocytes normally exhibit low membrane water permeability, making them useful for functional analysis after a candidate RNA is obtained.
- 3.Reconstitute purified protein into phospholipid vesicles and compare with protein-free liposomesconfirmatory biophysical assay
Test whether the purified protein alone is sufficient for selective water transport.
This confirmatory step follows heterologous expression to rule out dependence on other cellular factors and directly measure permeability and selectivity.
Taxonomy & Function
Primary hierarchy
Technique Branch
Method: A concrete measurement method used to characterize an engineered system.
Techniques
Functional AssayTarget processes
No target processes tagged yet.
Implementation Constraints
cofactor dependency: cofactor requirement unknownencoding mode: genetically encodedimplementation constraint: context specific validationoperating role: sensor
It requires Xenopus oocytes, injected cRNA for the candidate channel, and a hypotonic or osmotic assay to measure swelling or permeability.; requires cRNA injection into Xenopus oocytes; requires osmotic swelling or related permeability readout
It does not by itself establish full physiologic relevance in native kidney tissue or settle disputed noncanonical transport functions.; the review frames it as a functional assay and does not claim it resolves all physiologic relevance questions
Validation
Cell-freeBacteriaMammalianMouseHumanTherapeuticIndep. Replication
Supporting Sources
Ranked Claims
Biochemical purification and functional reconstitution techniques have been used to identify and characterize multiple transporters.
Using biochemical purification and functional reconstitution techniques, multiple transporters have been identified and characterized.
Proteoliposome reconstitution with fluorescence-based volume measurement can directly quantify water permeability of purified AQP1 and distinguish it from protein-free liposomes.
The change in volume of AQP1 proteoliposomes was compared to liposomes containing no reconstituted protein by measuring quenching of internal carboxyfluorescein.
The Xenopus oocyte expression system is a valuable method for functional analysis of candidate water channel RNAs because oocytes normally have low membrane water permeability.
the Xenopus oocyte expression system has proven to be a valuable method for functional analysis of candidate water channel RNAs, since the oocytes normally exhibit low membrane water permeability
Approval Evidence
1 source1 linked approval claimfirst-pass slug xenopus-oocyte-expression-system
The Xenopus oocyte expression system has proven to be a valuable method for functional analysis of candidate water channel RNAs, since the oocytes normally exhibit low membrane water permeability.
Source:
method utilitysupports
The Xenopus oocyte expression system is a valuable method for functional analysis of candidate water channel RNAs because oocytes normally have low membrane water permeability.
the Xenopus oocyte expression system has proven to be a valuable method for functional analysis of candidate water channel RNAs, since the oocytes normally exhibit low membrane water permeability
Source:
Comparisons
Source-stated alternatives
The review contrasts this expression assay with biochemical purification, functional reconstitution, and proteoliposome-based biophysical measurements.
Source:
The review contrasts this expression assay with biochemical purification, functional reconstitution, and proteoliposome-based biophysical measurements.
Source-backed strengths
oocytes normally exhibit low membrane water permeability; review describes it as a valuable method for functional analysis
Source:
oocytes normally exhibit low membrane water permeability
Source:
review describes it as a valuable method for functional analysis
Compared with Langendorff perfused heart electrical recordings
Xenopus oocyte expression system and Langendorff perfused heart electrical recordings address a similar problem space.
Shared frame: same top-level item type
Strengths here: looks easier to implement in practice.
Compared with native green gel system
Xenopus oocyte expression system and native green gel system address a similar problem space.
Shared frame: same top-level item type
Strengths here: looks easier to implement in practice.
Xenopus oocyte expression system and sub-picosecond pump-probe analysis of bacteriorhodopsin pigments address a similar problem space.
Shared frame: same top-level item type
Strengths here: looks easier to implement in practice.
Ranked Citations
- 1.